One of the typical conventional color image readers has such a structure that a document to be read is illuminated by a white light emitted from a single source thereof, the reflected light from the document is separated into three primary colors and each separated light is received by each image sensor formed with a linear array of micro charge coupled devices (CCD).
In another type of the conventional color image reader, there is provided a single light source of white color, three color filters provided for passing red, green and blue lights therethrough respectively and one image sensor constituted with CCD wherein lights having been filtered by three color filters respectively are sequentially projected onto the image sensor.
It is not impossible to read an image in a black and white mode with use of such a color image reader as mentioned above. In order to do that, it becomes necessary to combine color data by suitable electric circuits which are obtained as the result of the separation of the reflected light into three primary colors.
However, a ROM (Read Only Memory) of extremely large volume is needed, if one tries to achieve such combination with use of ROM or additional circuits. Also, if one tries to achieve such a combination with use of an electric computer, it takes much time in translating color data into black and white data and, therefore, the reading velocity is slowed down.
Moreover, the color reader will be further complicated and large scaled if one tries to obtain black and white data having been combined after changing a balance between color data that is to be enhanced and color data that is to be diminished.